Conventionally, plywood form panels in which battens are nailed to the rear surface of a sheathing panel made of veneer plywood or the like, are commonly used as form panels for placing concrete they are low cost, can be nailed easily, and are lghtweight.
However, disadvantages of these plywood form panels are that (i) a nailing operation needs to be performed when securing the battens or connecting form panels, causing poor workability, (ii) the form panel is easily damaged by the nailing, and by concrete stripper applied to the front surface of the sheathing board, and as such can only be reused a limited number of times (approximately 5 times, for example), and (iii) form panels which can no longer be reused cannot be recycled as wood, and can only be dismantled and incinerated.
In order to solve the above problems, a recyclable plastic form panel which is lightweight and has good workability has been proposed.
FIG. 17 shows an example of such a plastic form panel. This form panel 10 comprises generally; a hollow sheathing section 12, one side of which forms a concrete placing surface 11, hollow side panel sections 13 bent out at right angles from both side edges of the sheathing section 12 on the opposite side of the sheathing section 12 to the concrete placing surface 11, and two hollow reinforcing panel sections 15 provided on a rear surface 14 of the sheathing section 12, which are parallel to the side panel sections 13. Here, the sheathing section 12, the side panel sections 13 and the reinforcing panel sections 15 are formed from hollow panels in which two panels 16 and a plurality of long reinforcing ribs 17 connecting these panels, are formed as an integrated unit.
The erection (installation) of this form panel 10 is described below with reference to FIG. 18.
First, a plurality of form panels 10 are lined up so that the outside surfaces 18 of the side panel sections 13 contact each other. Next, round separators 22 with P-Cones 21, which are clips for maintaining a predetermined gap between the opposing form panels 10, provided near both ends thereof, are passed through insertion holes 20 formed in the sheathing section 12 of the form panel 10.
Next, clamps 23 called Form Ties (registered trademark) are screwed onto the ends of these separators 22, and the form panel 10 s secured by sandwiching the sheathing section 12 between the P-Cone 21 on the separator 22 and a template 24 at the base end of the clamp 23.
In the same manner, another set of a plurality of form panels 10 are lined up with the separators 22 inserted through the insertion holes 20, so that the concrete placing surfaces 1 pose each other. The clamps 23 are then screwed onto the ends of the separators 22, and the form panel 10 is secured, by sandwiching the sheathing section 12 between the P-Cone 21 on the separator 22 and the template 24 at the base end of the clamp 23.
In addition, a pair of walers 25 made from square pipe steel are provided above and below the clamp 23, and are secured by a clip plate 26 and a wedge 27 which fastens the clip plate 26, so that the walers 25 are in contact with the sides of the side panel sections 13 and the reinforcing panel sections 15. These walers 25 are provided to ensure that the form panel 10 does not expand outward due to the pressure of the concrete when the concrete is placed.
However, because the sheathing section 12 of this form panel 10 is a hollow panel in which two thin panels 16 (of thickness approximately 2 mm) and reinforcing ribs 17 which connect between these panels are formed as an integrated unit, the strength of the panels 16 is not sufficient to withstand the pressure applied by the P-Cones 21 and the template 24 of the amp 23 provided at both sides of the sheathing section 12. Consequently, when formwork fittings which tend to concentrate pressure on a single point are used, such as the P-Cones 21 and the clamps 23 used with conventional plywood form panels, then the form panel 10 is easily damaged. For such reasons, the use of these conventional formwork fittings with plastic form panels is problematic, and it is necessary to use special fittings with a specific shape. Accordingly, the installation of plastic form panels in the configuration sown in FIG. 18 is difficult to achieve. Furthermore, the inability to use conventional formwork fittings has hindered the popularization of these plastic form panels.
Moreover, in order to prevent poured concrete from leaking outside the form panel 10 through gaps between the contacting portions of the side panel sections 13, the outside surface 18 of the side panel sections 13, which is the surface in contact with the adjacent form panel 10, must be flat. However, since the form panel 11 is a large scale molded product which is formed as an integrated unit by means of extrusion molding, it is difficult to ensure that the outside surface 18 of the side panel sections 13 is completely flat, and furthermore, sometimes sight deformations can occur in the side panel sections 13 later repeated use of the form panel 1.
A form panel in which horizontal insertion grooves are provided in the outside surface of the side panel sections, and the separators are passed through insertion holes formed when the insertion grooves from adjacent form panels face each other when the outside surfaces of the side panel sections are aligned, is disclosed in Japanese Unexamined Patent Application, First Publication No. 200-8607, as an example of a form panel in which it is not necessary to provide insertion holes for separators in the sheathing section.
However, for the same reasons as for the form panel 10 described above, in this form panel there is still a danger of the poured concrete leaking outside the form panel due to gaps occurring between e contacting portions of the side panel sections. Furthermore, a flaw of these arm panels is that because it is necessary to provide insertion grooves, the form panel cannot be hollow, and consequently it is difficult to reduce the weight of the form panel.
Moreover, because it is necessary to provide insertion grooves across the entire surface of the side panel sections, forming the insertion grooves is time consuming.
Accordingly, an object of the present invention is to provide a recyclable plastic concrete form panel which enables the use of the formwork fittings such as the P-Cones and Form Ties (registered trademark) used in the conventional plywood form panels made of veneer plywood or the like, is light and has high workability, is durable, and does not suffer from problems of concrete leakage.